RFIDs have numerous uses, including, for example, inventory tracking.
RFIDs are utilized in systems with interrogators. The interrogators communicate with the RFIDs through radio-frequency (RF) signals. The RFIDs can be either active devices or passive devices. Active devices have their own power sources, and passive devices rely solely on power from RF signals sent by the interrogators.
Active devices have an advantage in that they can be utilized further from an interrogator than passive devices, but have the disadvantage that the power source within the active devices has a limited lifespan. Also, active devices can be more expensive than passive devices. Accordingly, passive devices and active devices each have advantages and disadvantages that can render one type of device more suitable for a particular application than the other.
Present RFID systems have sufficient communications range between tag and reader such that it is possible that many tags can be present at one time within a reader antenna working volume. Thus, when the interrogator reads a tag, the user may not be able to determine which tag has been read. It could be one of many because there is no visible indicator of which tag ID corresponds with which physical tag. There exist applications, such as inventory management, where an ID number relates to one specific part. Any uncertainty or ambiguity in such systems may destroy the integrity of the inventory tracking system. Because passive tags have no power absent a reader, it has been problematic to provide a visual indicator means that persists in the absence of incident reader power on a passive tag.